A present method of generating power on aircraft is through an Auxiliary Power Unit (APU). APUs are used on airliners to provide electricity when the main engines are off (e.g. to run the air conditioning while passengers are boarding). These systems consist of a small gas turbine engine connected to a wound-field synchronous generator. This class of generator is desirable because the output voltage of the generator can be regulated by servoing the current in the field winding. So that the generator does not have endure high rotational stress, the generator is typically coupled to the engine through a speed-reducing gear box.
However, the power level of most APUs is low compared to that required to operate Directed Energy Weapons (DEWs). To reduce generator weight for DEW applications, it is desirable to directly couple the generator to the gas turbine, since power density of an electric machine goes up roughly linearly with rotational speed. Wound field machines have a complicated rotor structure. Most machines have a windings and a rectifier bridge located on the rotor, and a separate exciter rotor section is needed to induce the DC field winding current on the rotor. It is difficult to make a wound-field rotor with the mechanical integrity required to run at high speeds.
Consequently, most high-speed generators disclosed in the literature are of one of three types: Surface-mount permanent magnet motor (PM), Induction motor (IM), and Switched reluctance motor (SRM). See, A. Arkkio et al., “Induction and Permanent-Magnet Synchronous Machines for High Speed Applications,” Proceedings of the Eighth International Conference on Electrical Machines and Systems, 29-29 Sep. 2005, incorporated herein by this reference.
The disclosed machine is in the general class of Doubly Salient or Flux Switching machines. Flux switching machines that are superficially similar to the presently disclosed machine are described in the literature. See, F. Liang, Y. Liao, and T. Lipo, “A new variable reluctance motor utilizing an auxiliary commutation Winding”, IEEE Transactions on Industrial Applications, 30(2):423-432, March/April 1994. http://lipo.ece.wise.edu/1992pubs/92-25T.pdf incorporated herein by this reference. See also, R. Cao et al.: A Linear Doubly Salient Permanent-Magnet Motor With Modular and Complementary Structure”, IEEE Transactions on Magnetics, 47(12):4809-4821, December 2011, incorporated herein by this reference. However, the presently disclosed machine has novel design differences that reduce cogging torque and produce better conditioned output voltage.